A typical conventional motor drive assembly used in electric vehicles or hybrid vehicles includes an electric motor, a transmission for changing the rotational speed of the electric motor, and a differential for distributing the rotation produced from the transmission to right and left vehicle wheels.
By changing the speed ratio of the transmission of this motor drive assembly according to the travel conditions, it is possible to use the electric motor at the optimum rpm and torque range both while the vehicle is being driven and during regenerative braking.
By using an optimum speed ratio, it is possible to minimize the rotational speeds of rotary members of the transmission and thus the power loss of the transmission, thereby improving the energy efficiency of the vehicle.
The below-identified Patent document 1 discloses a vehicle transmission of the below-described type.
A transmission including an input shaft to which the rotation of an engine is applied, a second-speed input gear and a third-speed input gear mounted on the input shaft, a second-speed output gear and a third-speed output gear meshing with the second-speed and third-speed input gears, respectively, an output gear carrying the second-speed and third-speed output gears, an electromagnetic multiple disk clutch provided in a torque transmission line extending from the engine to the input shaft,
wherein the second-speed and third-speed input gears are rotatably supported by bearings, respectively,
a second-speed two-way roller clutch through which torque is selectively transmitted between the second-speed input gear and the input shaft, a third-speed two-way roller clutch through which torque is selectively transmitted between the third-speed input gear and the input shaft, and a shifting actuator for selectively engaging either one of the second-speed two-way roller clutch and the third-speed two-way roller clutch,
wherein the second-speed two-way roller clutch includes a cylindrical surface formed on the inner periphery of the second-speed input gear, cam surfaces formed on the outer periphery of the input shaft, rollers disposed between the cam surfaces and the cylindrical surface, a second-speed retainer retaining the rollers and rotatable relative to the input shaft between an engaged position where the rollers are engaged between the cam surfaces and the cylindrical surface and a neutral position where the rollers are disengaged, and a switch spring biasing the retainer toward the neutral position,
wherein the third-speed two-way roller clutch is similar in structure to the second-speed two-way roller clutch, and
wherein the shifting actuator includes a second-speed friction plate rotationally fixed to the retainer on the second-speed side and axially movable between two positions in contact with and away from the side of the second-speed input gear, a separation spring biasing the second-speed friction plate away from the side of the second-speed input gear, a third-speed friction plate rotationally fixed to the retainer on the third-speed side and axially movable between two positions in contact with and away from the side of the third-speed input gear, a separation spring biasing the third-speed friction plate away from the side of the third-speed input gear, a shift ring axially movable between a second-speed shift position where the shift ring presses the second-speed friction plate against the side of the second-speed input gear and a third-speed shift position where the shift ring presses the third-speed friction plate against the side of the third-speed input gear, and a shift mechanism for axially moving the shift ring.
With this transmission, while the shift ring is in the second-speed shift position, due to the frictional force between the side of the second-speed input gear and the surface of the second-speed friction plate in contact with the side of the second-speed input gear, the second-speed friction plate rotates relative to the input shaft, thus rotating the retainer on the second-speed side, which is rotationally fixed to the second-speed friction plate, from the neutral position to the engaged position. The second-speed two-way roller clutch thus engages.
By axially moving the shift ring of this transmission from the second-speed shift position to the third-speed shift position, it is possible to disengage the second-speed two-way roller clutch and engage the third-speed two-way roller clutch, in the following manner.
When the shift mechanism is activated and the shift ring begins to move axially from the second-speed shift position toward the third-speed shift position, the second-speed friction plate separates from the side of the second-speed input gear under the biasing force of the separation spring. This allows the retainer on the second-speed side to return to the neutral position from the engaged position, disengaging the second-speed two-way roller clutch.
When the shift ring reaches the third-speed shift position, and thus the third-speed friction plate contacts the side of the third-speed input gear, the third-speed friction plate rotates relative to the input shaft due to the frictional force between the contact surfaces, thus moving the retainer on the third-speed side, which is rotationally fixed to the third-speed friction plate, from the neutral position to the engaged position. The third-speed two-way roller clutch thus engages.
Conversely, by axially moving the shift ring from the third-speed shift position to the second-speed shift position, it is possible to disengage the third-speed two-way roller clutch and engage the second-speed two-way roller clutch.